Method of forming hobs



July 14, 1925.

E. WILDHABER mn'ruonbr' FORMING HOB S Filed June a, 1922 5 Sheets-Sheet1 ATTORNEY July 14, 1925; 1,545,719

E. WILDHABER METHOD OF FORMING HOBS Filed June 8, 192g 5 Sheets-Sheet 2INVENTOR ATTORNEY July 14, 1925. 1,545,719

E. WILDHABER METHOD OF FORMING HOBS Filed June a, 1922 5 Sheets-Sheet sAW J 6 l 71 INVENTOR ATTORNEY July 14, 1925. 1,545,719

\ E. WILDHABER METHOD OF FORMING HOBS Filed June 8, 1922 5 Sheets-Sheet4 INVENTQR ATTORNEY July 14, 1925. 1,545,719

E. WILDHABER METHOD OF FORMING HOBS Filed June 8, 1922 5 Sheets-Sheet 5ATTORNEY Patented July 14, 1925.

UNITED STATES PATENT. OFFICE.

ERNEST WILDHAIBER, OF BROOKLYN, NEW'YOBK, ASSIGNOR T NILES-BEMIlNT- PONDCOMPANY, OF NEW YORK, N. Y., A. CORPORATION OF NEW JERSEY.

un'rnon or some noes.

Application filed June 8, 1922. Serial No. 566,855.

To all wkomitmay concern: 7

Be it known that I, ERNEST WILDHABER, a citizen of the Republic ofSwitzerland residin at Brooklyn, in the county of Kings and tate of NewYork, have invented certain new and useful Improvements .in Methods ofForming Hobs, of which the following is a specification. v

-My invention relates to methods of forming rotating tools andparticularly to methods of forming and relieving hobs and millingcutters. a

Oneobject of my invention is to provide a method of forming rotatingtools by a continuous milling operation that shall relieve the teeth onthe tool in a quick and an efii-.

cient manner.

Another object of my invention is to provide a method of forming a hobby a hobbing process that shall consist in rotatin a master hob and ablank in engagement w1th each other and in opposite directions, and-inefl'ecting angular advancing and feeding movements between the hobandthe blank for relieving the teeth being formed on the latter. 7 I

Another object of my invention is to provide a method of forming a hobthat shall consist in providing a master hob having teeth formed byveither axial or inclined flutes, in rotating the hob in engagement witha blank having flutes similar to the hob flutes, the blank flutes beinginclined oppovsitely to-the hob fiutes if the hob flutes are inclined,the blank and the hub being rotated in opposite directions and incertain cases at the same angular speed, in efl'ectin angular advancingmovements by the ho with respect to the blank, and in effecting feedingmovements of the hob with respect to the blank for relieving the teethbeing formed'on the latter. Another object of my invention is to pro.-

vide a method of forming a hob, that shall consist in providing a masterhob havin teeth formed in a right handor a left han thread by means ofaxial or inclined flutes, in rotating the hob in engagement with a blankhavlng flutes .formed in it similar to the hob flutes, the blank flutesbeing inclined oppositely to the hob flutes if the latter are inclined,and informing-a thread onthe blank of an opposite hand to the hob threadwhile feeding and angularly advancin the hob with respect to the blankfor re loving the teeth being formed on the blank.

A further object of my invention is to provide a method of forming a hobthat shall consist in roviding a hob having teeth formed therein yflutes, in rotating the hob in engagement with a blank having similarflutes formed in it, the blank and the hob bemglrotated in oppositedirections, in feed.- ing t e hob towards or away from the blankaccording to the position of the hob teeth with respect to the teeth tobe formed on the blank, and in angularly advancing the hob with respectto the blank, such feeding and advancmg movements being effected intimed relation to each other.

At the present time, it is customar to form either a thread hob or agear holi by means of a formed lathe tool or a milling cutter. In case aformed lathe tool is utilized for shaping the thread milling hob onlyone thread can be formed on the hob at a time, and consequently, theprocess is somewhat tedious and slow. Moreover, in such a process eachtooth is separately relieved by the lathe tool., A thread milling hobmay be formed by a formed milling cutter in substantially the same stepsas when forming such a hob by a formed lathe tool. In vcase a hob isshaped by a formed lathe tool, it is preferable first-to form a threadon the hob and then to cut the flutes.

tomary and usual manner by means of the formed lathe tool. It should benoted that in the method now in use only one side of each of two teethcan be relieved simultaneously. When forming a hob by means of a formedmilling cutter, the flutes may be cut in the blank prior to the-formingof the coidal thread hobs above method. t

In forming a hob in accordance with my invention, a master hob isprovided for forming a blank by a continuous operation. The blank, whichis provided with flutes similar to the flutes on the master hob, isromay be formed by the tated in engagement with the master hoband in anopposite direction. The master hob engages the blank along the completelength and forms relieved teeth thereon'in an efiicient manner. Itshould be noted that The teeth thus formed in the thread are relievedinthe cusa number of teeth are relieved on the blank simultaneously andthat the operation is continuous. The master hob is similar in shape tothe hob to be formed. However, the master hob is in certain cases largerin diameter than the blank in order to effect a cutting action whenrotated in engagement with the blank. The blank is provided with flutessimilar to the flutes on the master hob but if the flutes on the masterhob are inclined, it is necessary to incline the flutes on the blank inan opposite direction. Moreover, if the master hob has a right handthread, a left hand thread will be cut on the blank. Therefore, whencutting certain types of hobs, it is necessary to provide the master hobwith a thread having an opposite hand to the hand which it is desired toform on the blank.

Although the master hob and the blank are rotated in opposite directionsand at the same angular speed, a cutting action is effected by the hob,as heretofore set forth, by making the diameter of the master hob largerthan the diameter of the blank. The teeth on the master hob should meshwith the teeth to be formed on the blank in the same manner as the teethon two gear wheels mesh with each other. In certain cases, the masterhob has the same number of flutes formed on it as are formed onthe-blank. However, in case a ring or a circular thread is formed on theblank by the hob, it is permissible to have more or less teeth on thehob as compared with the teeth formed on the blank. If a differentnumber of flutes are formed on the blank as compared with the flutes onthe master hob, it is necessary to vary the speed of a hob in accordancetherewith.

Although the master hob and the blank mesh in the manner of twogear-wheels, it is necessary to vary the size of the hob and the blankas compared with corresponding gear wheels in order not to obtain a purerolling action between them. It is apparent the peripheral speed of thehob must be different from the peripheral speed of the blank in order toobtain a cutting action. Accordingly, the master hob is generally made alittle larger than the pitch diameter of the corresponding gear wheel.The ratio of rotation of the hob and blank must be maintainedsubstantially constant in order to insure the meshing or engagement ofeach hob tooth with the corresponding tooth being cut in the blank.

During the rotation of the hob with the blank, relative advancingmovements are effected between the blank and the hob for forming athread. Preferably, the hob is continuously and angularly advanced aslight amount in conformity to the rotation of the-blank. Such actionmay be accomplished by so gearing the master hob to the necessary tofeed the blank and the hob toward each other. Preferably, the hob iscontinuously fed towards the blank in any suitable manner and in timedrelation to the blank rotation.

If the teeth on the master hob and the .blank face in thesame direction,it is necessary to relatively move the blank and the hob away from eachother to relieve the teeth on the blank. Preferably, the hob is movedaway from the blank by a continuous feeding movement and in timedrelation to the blank rotation. In such latter case, it is unnecessaryto relieve the teeth on the master hob with the accuracy it is necessaryto relieve the teeth on a hob when the hob teeth and blank teeth face inopposite directions.

However, it is necessary to have the cutting edges accurately formed. Ifso desired, when the blank and the hob teeth face in the same direction,the hob teeth may be roughly relieved and be provided with unrelievedground surfaces adjacent to the cuttingedges.

The blank and the hob are preferably axially moved with respect to eachother in case a thread with lead is to be formed on the blank.Preferably, the master hob is fed axially with respect to the blank. In

most cases the master hob is single threaded and the blank is alsosingle threaded and in such case the lead of the master hob must beequal to the lead formed on the hob blank. If the hob blank has nthreads and the master hob has M threads, the lead of the master hob istimes the lead of the hob blank. Accordingly, the revolutions of themaster hob are substantially times the number of revolutions of the hobblank.

The master hob mayrelieve the teeth on the blank by radial relief oraxial relief or a combination of axial and radial relief. Preferably,the teeth on the blankare relieved by the so-called radial relief.Radial relief is preferred to axial relief ora combination of axial andradial relief inasmuch as the teeth may be relieved in one operation. Incase the teeth are relieved by axial relief, it is necessary to relieveone side of the teeth by one operation and to relieve the opposite sideof the teeth of the blank by another operation.

' If so desired, the fluteson' the hob and the blank may 'form undercutteeth. Moreover, the axis of thejhob may be elevated with respect to theaxis of the blank, if so desired. The elevation of the master hob willcut involute helicoidal surfaces on the teeth of the blank. In case thehob blank is provided with involute helicoidal surfaces, such surfaces.can be ground with ease and accuracy.

In the accompanying drawings:

Figure 1 is a diagrammatic, view of a blank being shaped by a master hobin accordance with my invention.

Fig. 2 is a plan view of the hob and blank shown in Fig. 1.

Fig. 3 is an end view similar to Fig. 1 and showing the blank teethnearly completed.

F ig. 4 is a diagrammatic plan view of a master hob and a blank havinginclined flutes.

Fig. 5, which is an end view of the hob and blank illustrated in Fig. 4,shows the axes of the hob and blank in diflerentplanes.

Fig. 6 is a diagrammatic view showing the relative movement of a cuttingpoint.

Fig. 7 is a diagrammatic plan view illustrating the cutting of a threadwith lead on.

a hob blank.

Fig. 8, which is an end view of the hob' ing the relation between siderelieving and radial relieving movements.

Fig. 12 is a diagrammatic plan view of a machine having a differentialgear mechanism for controlling the feeding movement.

Fig. 13 is an end view of the machine shown in Fig. 12.

Referring to Fig. 1 of the drawings, a hob 1 is shown in engagement witha blank 2. The hob 1 comprises teeth 3.to 10, inclusive, which areformed by means of axial flutes 11. The hob is assumed to rotate on anaxis 12 in a clockwise direction as indicated by the arrow a. Thecutting faces 21 of the teeth 3 to 10, inclusive, are assumed to face inthe direction of rotation of thehob.

The blank 2 comprises teeth 13 to 20, in-

clusive, which are formed by means of flutes 22. Completed blank teethhave been shown in Fig. 1 of the drawings for more clearly illustratingmy invention.' The flutes 22 are assumed to be axial and the teeth 13 to20, inclusive, are assumed to respectively engage the teeth 3 to 10,inclusive, of the master hob. The blank is assumed to rotate on' an axis23 in a counter clockwise direction as indicated by the arrow a. Theflutes 22 on the blank and also the relief which is formed on the topsof the teeth 13 to 20, inclusive, may be effected by means of a formedmilling cutter, if so desired. By so relieving the tops of the blankteeth approximately to size, it is possible to shape and relieve teethon the blank very quickly by the master hob. However, it is to beunderstood that, if so desired, the flutes 22- in the blank may be.first cut and then the teeth may be completely shaped and relievedbymeans of a master hob.

The master hob 1 and-the blank 2 are rotated at the same angular speedin order to obtain engagement between the teeth 3 to 10, inclusive, onthe hob with the teeth 13 to 20,

inclusive, being formed on the blank. Inasmuch as the hob 1 is larger indiameter than the blank 2, a cutting action takes place between them. Itwill be noted that the hob and the blank engage each other somewhat inthe manner of two meshing gear; wheels.

However, the diameter of the hob must be made somewhat larger than thepitch diameter of a corresponding gear wheel'in order to prevent truerolling action between the hob and the blank. Inasmuch as the hob andblank rotate at substantially the same speed, it is necessary toangularly advance the hob .in order to effect a out along the completelength of each tooth. At the same time as the angular advancing movementis efi'ected by the hob, the hob is fed towards the blank in order toproduce relief on the blank teeth. The angular advancing movement andalso the feeding movement should be effected in timed relation t therotation of the blank and thehob. siich movements may be effected eitherby the hob or by the blank.

loo-

The hob and the blank must rotate in timed relation to each other in.order to, efl'ect correct engagement between the teeth of the hob andthe teeth of the blank.

Although the hob and the blank rotate at thesam'e angular speed, it isapparent the peripheral speed of the teeth on the hob is greater thanthe peripheral speed of the teeth being formed on the. blank,accordingly as heretofore set forth, a cutting ac- Y tion takes place onthe blank. The path of movement of a cutting point on the hob isindicated by the arrow E in Fig. 1 of the drawings. The teeth ontheblankface in an opposite direction as compared with the "teeth on thehoband for this reason, the hob is fed towards the blank in order to re- Ifthe blank teeth lieve the blank teeth. faced in an opposite direction,it would be necessary to feed the hob and the blank away from each otheras willbe explained in connection with FigXS-of-the' drawings.

Referringl'to' Fig. 3 got the drawings. it will be noted the hob 1 hasbeen-fed forward a distance A to relieve the teeth on the blank. Theteeth 13 to 20, inclusive, on

the blank shown in Fig. 3, have been completely shaped and relieved withthe exception of a small shaded portion 24 shown at the end ofeachtoothf Such shaded portion will be cut away when the hob isangularly advanced a small amount. The arrow E indicates. the path'ofmovement of a cutting point on the hob and it will be noted that suchpath of movement is so curved as to prevent any interference between thehob teeth and the blank teeth adjacent to the tooth being cut. Thus,each hob tooth cuts one blank tooth and in, no way interferes with theadjoining blank teeth. The path of movement of a cutting point on thehob will be further'discussed when reference is made to Fig. 6 of thedrawings. However, it should be noted that the relative path of movementof a cutting .point on the hob is very sharply .curved. Consequently,the teeth of the hob may be. made large and strong. Such large hobs,operated in accordance with my invention, clear the adjoining teeth on ablank much better ithan a milling cutter of a much smaller size whenoperated according to the usual practice. Moreover, attention is calledto the fact that no reciprocating movement is necessary in order torelieve the teeth being formed on the blank. One continuous feedingmovement in one direction only is all that is required for relieving andforming the teeth on the blank. Thus, the ordinary cam, which isprovided for relieving the teeth on a hob blank, is eliminated as wellas the var-ions movements controlled thereby.

Although a ring hob having axial flutes is illustrated in Figs. 1, 2 and3 of the drawings, it is to be understood that the hob flutes may beinclined in either direction if so desired. However, if the hob flutesare inclined, it is necessary to provide similar flutes in the blankwhich are inclined in an opposite direction. If the thread on the masterhob is provided with a lead, a similar thread will be formed on theblank with the lead in an opposite direction. The master hob may havesingle, double or any number of threads formed on it. The variousthreads may be formed on the blank in accordance with the relativerotation of the hob and the blank and in accordance with the number ofthreads on the hob. The forming of helical threads will be morespecifically described when reference is made to Figs. 7 and 8 of thedrawings. Attention is also called to the fact that the relative speedbetween the hob and the blank may be so varied that each tooth on thehob cuts more than one tooth on the blank. Moreover, the master hob maybe provided with interrupted or staggered teeth which will out similarstaggered or interrupted teeth on the blank. Although threaded hobs havebeen shown in the drawings, it is to be understood that other hobs andparticularly gear hobs may be made in a similar manner.

Referring to Fig. 6 of the drawings, the relative movement of a cuttingpoint on a master hob with respect to a blank will be considered. Ablank 26 shown in Fig. 6 is assumed to have the same number of 'roovesas a master hob 27 and to be rotate at the same angular speed. The hoband the blank for simplicity are indicated by their pitch circles. Themaster hob is assumed to rotate on an axis C and the blank is assumed torotate on an axis C. Although in practice, the blank and the hob wouldrotate in opposite directions, as indicated b the arrows (1 and a inFigs. 1 and 6 of t e drawings, it is assumed that the blank 26 remainsstationary while the hob not only rotates on its axis 0 but alsorevolves around point P is closest to the center C of: the

blank 26 when in position P and on a line passing through the axes G andC. In order to move the point P to such position, the line PC must beturned through an angle PCC'. In other words, the master hob must berolled or revolved through the angle F00. The axis C of the master hob27 assumes a Iposition indicated by the charaeter C n such position ofthe hob and the blank, the angle C -CC must equal the angle PCC'. It isapparent that the point P is closest to the center of the blank for theline CC passes through the centers of the hob and the blank.

The axis C of the hob 27 may be assumed to be revolved to any newposition C The position P of the point P corresponding to the newposition of the hob with respect to the blank is determined by makingthe angle P 0 0 equal to the rolling angle QC'C of the hob and byplotting the distance GP on the line C Q. The line tangent the pitchcircle of the blank 26 at the inangle P C C' is'equal to the angle C 0 GAny other position of the point P may be determined in like manner andthe complete Ill curve E may be plotted, as indicated in Fig. 6 of thedrawings. In the above example, it is assumed that the master hob andthe blank have the same numberof flutes and the ratio of rotation of thehob and the blank is substantially one to one. If the number of fluteson the blank is varied as compared to the number of flutes on the hoband the speed ratio between the hob and blank. is varied, the abovemethod of plotting the path ofmovement of a point P must be varied inaccordance therewith.

In examining the curve E as indicated in Fig. 6 of the drawings-it isapparent the cutting point engages and disengages the blank very rapidlyand along a. very sharp curve. Consequently, it is possible to make themaster'hob comparatively larger in diameter as compared to the blank andin no way to obtain interference betwe n the hob teeth and the blankteeth other than the tooth which is being cut.

Referring to Figs. 4 and 5, a master hob 30 is shown in engagement witha blank 31. The blank 31 is assumed to rotate on an axis 32- in acounter-clockwise direction as indicated by the arrow a. The hob 30rotates on an axis 33 which is located a distance b above the axis 32 ofthe blank 31. The hob is provided with six teeth 34 to 39, inclusive,whereas the. blank is provided with twelve teeth 44 to 55, inclusive.The hob 30 is provided with spiral flutes 56 and the blank 31 isprovided with spiral flutes 57 It will be noted, as shown in Fig. 4 ofthe drawings, that the spiral flutes 56 and 57 extend in oppositedirections. The hob 30 rotates in a clockwise direction as indicated bythe arrowa.

Inasmuch as the hob 30 is provided with half as many teeth as the blank31, it is necessary to vary the speed ratio between th hob and the.blank in accordance with b such difference inthe number of teeth onthem. The tooth 34 on the hob 3O not'only cuts and shapes the tooth 44on theblank but also cuts and shapes the tooth 50 on the blank. Thetooth 35 on the hob cuts and shapes the teeth 45 and 51 on the blank. Inlike manner each of the remaining teeth on the hob cut and shape twoteeth on the blank. Although spiral flutes have been shown with the hobhaving a less number of teeth than the number of teeth on the blank andwith th hob having the axis thereof levated above the axis of the'blank,it is to be understood that spiral flutes may be provided on anysuitable hob and blank. It should also be noted that although threadhobs have been. adapted for illustrative purposes, it is to beunderstood that my invention is in no way limited to such type of hobsand that the various features described are equally adapted to otherhobs such for example, as gear cutting hobs.

blank teethface in I tion as the teeth on the hob. In .the hob and Inthe arrangement shown in Fig. 5 of the drawings, theteeth onthe blankand the teeth on the hob extend in opposite directions and, accordingly,it is necessary to feed the blank and hob towards each other in order torelieve the teeth on the blank Although the arrow F indicates the hob ismoved towards the blank, it is to be understood that the blank may befed towards the hob if so desired. a

In moving the hob in a plane other than a plane directed towards theaxis of the blank, it is possible to provide a blankwith involuterelieved curves. The above statement is true not only for circular orring hobs but also for helicoidal hobs. It is necessary, however, tomake a difl'erent setting for each of the types of hobs. It may also benoted that in order to out true involute helicoidal relieved surfaces onhelicoi dal hobs, it is necessary to make a different setting for eachsideof the teeth. The two sides of the teeth therefore can only be cutone after the other. It will be noted that involute helicoidal surfacescan be ground with ease and accuracy and it is possible to figure outvarious corrections as for example, against spiral flutes or' undercutteeth if involute relieved surfaces are provided.

Preferably, the master hob and the blank are provlded with undercutteeth in order to improve the cutting action and moreover, it ispreferable to have the teeth of the master hob ground. When the hob andthe blank. are provided with undercut teeth, it is found desirable toslightly correct the cutting angles of the master hob in order to obtainexact cutting angles on the blank. The corrections which are made to thehob teeth depend upon the amount of relief, the amount of undercut andthe lead of the flutes, such corrections may be determined y experiment,if so desired, or may be fig ured mathematically. Moreover, it should benoted that the corrections are different for the two sides of the hobwhere helicoidal hobs are used. The mathematical dc terminations of thecorrections necessary. to be made to the master hob are very long and.it is believed unnecessary to discuss and explain the same. Suchcorrections may bedetermined experimentally with little trouble.

In Figs. 7 and 8 of the drawings, a hob 60 is shown operating'inengagement with a blank 61. The hob 60 rotates in .a clockwise directionon an axis 62, as indicatedby the arrow a. The blank 61 rotates on anaxis 63 in a counter-clockwisedirection, as indicated by the arrow a,The hob 60 is provided with eight teeth 64 to 71, inclusive, whichengage eight teeth 74 to 81, inclu sive, on the blank. It will be notedthat the exactly the same direccated in Fig. 8 of the drawings.

blank shown in Figs. 1, 2 and 3 of the drawings, the hob and blank teethface in opposite directions. The hob 60 is provided with axial orstraight flutes 82 and the blank 61 is provided with similar flutes 83.

The teeth on the master hob are arranged in the form of a left handthread, as indicated in Fig. 7 of the drawings. The teeth being formedon the blank are arranged in the form of a right hand thread. Inasmuchas the thread on the blank extends in an opposite direction to thethread on the hob, it is necessary to provide the master hob with athread in an opposite hand to that which it is desired to form on theblank. Al

though, the thread with lead is illustrated with the hob 60 havingstraight flutes, it is to be understood that a hob and blank may operatein exactly the same manner and be provided with spiral flutes orinclined flutes extending through the helicoidal thread.

lrVhen the cutting faces of the hob and blank face in the samedirection, it is much preferable to begin the relievlng of the blankteeth at the inner end of each tooth. The starting of a relievingoperation is indi- In order to relieve the teeth on the blank, it isnecessary to move the hob and the blank away from each other in timedrelation to their rotation. By so relieving the blank when the faces ofthe teeth on the blank and the hob face in the same direction, it ispossible to operate the master hob without formin any exact reliefthereon. The teeth of the hob may be provided with ribbons 85 ofunrelieved surfaces. Such ribbons may be formed on the hob by contourgrinding and preferably such ground surfaces conform to an involutehelicoidal thread. Byso forming the ground surfaces, it is possible togrind such surfaces with little trouble. It is preferable, however, tocut the teeth of the hob back of the front cutting face in order toprevent interference between the hob teeth and teeth on the blank otherthan the tooth which is being operated upon. Such cutting away of thehob back of the cutting face does not need to conform to anypredetermined relief. The relief on the blank teeth is formed by themovement of the hob and the blank away from each other. The hob ismovable away from the blank in timed relation to the blank and hobrotation.

In forming a helicoidal hob in accordance with my invention, the tworelieved side surfaces of each tooth are out with the .same master hoband simultaneously. It is not only necessary to provide radial feedingmovement for relieving the teeth being formed on the blank but it isalso necessary to provide an axial or lead movement in accordance withthe lead of the hob thread. If the axial movement does not correspond tothe lead of the continuous hob thread, the

two sides of the teeth will not be equally relieved. One side of eachtooth will be more relieved as compared with the continuous thread.

As shown in Fig. 7 of the drawings, it is always necessary to provide amaster hob wlth a thread of the opposite hand to the thread which is tobe cut on the blank. In the majority of cases, the master hob is madesingle threaded, as shown in Fig. 7 of the drawings. If the blank isalso single threaded the lead of the master h b must be made equal tothe lead of the hob blank. Generally, if the blank has n threads and themaster hob has m threads, the lead of the master hob will be times thelead of the blank.

master hob is substantially times the The number of revolutions of theand axial relief may be provided, if so deg sired. Referring to Fig. 11of the drawings, a radial relieving movement of the hob with respect tothe blank is indicated by the line AB. In other words, the hob isadvanced or withdrawn with respect to the blankalong the line AB for adistance corresponding to the length of the line AB.

In like manner an axial relieving movement will correspond to the lineAB. A combined relieving movement would be in a direction correspondingto the line AB. Very nearly the same effect would be accomplished byutilizing any one of the three different kinds of relieving movements.

In case the blank is relieved by an axial relieving movement, the masterhob is advanced axially corresponding to the lead of the master hob plusor minus the lead due to the relief depending on the side which is beingcut. The two sides of each tooth are therefore ,cut one after the other.However, it is possible to simultaneously cut one blank by means of twohobs. lVhen providing side relief or axial relief, the relieved surfacesthus obtained are parts of helicoidal surfaces. If the cutting edges ofthe master hob are parts of the involute helicoidal surfaces, then ablank will be formed in accordance with involute helicoidal surfaces.Radial relief is usually preferred to axial relief because the two sidesof the teeth can be relieved simultaneously.

Referring to Figs. 9 and 10 of the drawings, a machine isdiagrammatically shown for shaping a blank in accordance with myinvention. The machinecomprlses a mam frame 90 having a longitudinallymovable slide 91 mounted thereon. The slide 91 carries a laterallymovable slide 92. The slide 92 supports a master hob 93 in any suitablemanner. .The master hob is rotated in a counter-clockwise direction, asindicated by the arrow 0; in Fig. 10 of the drawings.

The master hob engages a blank 94 which is 102, which meshes wth thegear wheel 101,

is fixedly mounted on a shaft 103. The shaft 103 is supported by arms104, 105 projecting from the slide 92 and an arm 106 pro ecting from theslide 91. An arm 107, which pro jects from the'slide 91, is providedwith a yoke-shaped end portion 108. The end por tion 108 engages thebevel gear wheel 101.- in order to cause such gear wheel to follow themovements of the slide 91. Thus, the

gear wheels 101 and 102 are always maintained in mesh with each otherregardlessof the position of the slide 91. The bevel gear wheel 102 isrestrained against longitudinal movement on the shaft 103 by means ofthe bracket 106 and a bolt which-is secured to the end of the shaft 103.A worm member 109 is keyed to but slidably mounted on the shaft 103. Theworm member 109 is located between the arms 104, 105 on the slide 92 inorder to follow the movements of the slide. A worm wheel 110, which ismounted on a shaft 111 connected to the hob spindle, meshes with theworm member 109. The shaft and spindle are provided with suitablebearings in the brackets 112 and 113 which project from the slide 92.

The shaft 99, which carries the pulley 98,

is connected to the shaft 114 through a set of change gears 115 whichare enclosed within the change gear box 116. The change gears 115 may beof any suitable type and are here shown as providing for three differentspeeds in a forward direction and one reverse speed. A detaileddescription of such change gears is deemed unnecessary. The shaft 114 isprovided with bearings in the bracket 96 and in the change gear box 116.A worm member 117 which is fixedly mounted on the shaft 114, meshes witha worm wheel 118 which is mounted on a short shaft 119. The worm wheel118 is mounted on the shaft 119 between two arms which project from themain frame of the machine The shaft 119 carries a bevel gear wheel 120which meshes with a bevel gear wheel 121 on a shaft 122. The shaft 122carries a gear wheel 123 which meshes with a gear wheel 124 on a shaft125. The shaft 125 is provided with the hearings in the bracket 96 andin brackets 126 and 127 which project from the main frame of themachine. A bevel gear wheel 128 is keyed to but slidably mounted on theshaft ,125 between the two brackets 126 and 127. The bevel gear wheel128 meshes with a bevel gear wheel 129 which is fixedly mounted on afeed screw 130. The feed screw 130 is provided with suitable bearings onthe slide 92 and is connected to the slide 92 by means of the suitablenut 131. Such feed screw serves to feed,the master hobtowards the blankin order to relieve the teeth being cut on the blank. An arm, whichprojects from the slide 92, engages .the bevel gear wheel 128 and causesit to follow the movements of the slideand to maintain the gear wheels128 and 129 inmesh with each other. A" gear wheel 132, which is mountedon the shaft 114 adjacent to the bracket 96, meshes with a gear wheel133 which is mounted on the blank spindle 95. Such connection serves toeffect rotation of the blank 94 in timed relation to the rotation ofthemasterhob 93.

.-'A. gear wheel 135, which is mounted on the shaft 122 between thebracket 96 and the gear wheel 123,. meshes with a'gear wheel 136 on ashort shaft 137. The shaft 137 is supported in the bracket 96 andcarries a second gear Wheel 138 which meshes with a gear' wheel 139 on afeed screw 140. The feed screw 140 serves to-efi'eot longitudinalmovement of the slide 91 in any suitable manner. It will. be noted theslide 91 op-' crates on a guide 141 and set screws 142 are provided forlocking the slide 91 in any set position. In case a thread without leadis being cut on the blank, it is necessary to lock the slide 91 againstany longitudinal movement.

The gear connections between the master hob and the source of power andbetween the blank and the source of power are so adjusted as to effectadvancing movement by the master hob. Thus, the speed of rotation ofthemaster hob is slightly greater than the speed of rotation of theblank in order to effect a continuedcutting action by the hob along theblank teeth. Inasmuch as the hob and the blank are geared directly tothe same source of power, it is apparent such members are rotated intimed relation to each other. Moreover, the gearing for effectingfeeding movement of the: hob toshaft 171.

wards the blank is connected to the same source of power andconsequently the feeding movements are effected in timed relation to therotation of either the hob or the blank.

In the machine illustrated in Figs. 9 and 10 of the drawings, the hoband the blank spindles are directly geared with each other at an unevenratio which corresponds substantially to the ratio of the number offlutes on the hob and the blank. In such a machine it is necessary tochange the gear wheels connecting the two spindles if a change in thefeed is desired. In the machine illustrated in Figs. 12 and 13 ofthedrawings, a differential gear mechanism is provided between the blankand the hob spindles in order to obviate the necessity of changing thegear connection between such spindles when a change in the feed isdesired.

Referring to Figs. 12-and 13 of the drawings, a machine is disclosedcomprising a main frame 150, a longitudinally movable slide 151 and atransversely movable slide 152 which is mounted on the slide 151. Theslide 151 operates on a guide 153 on the main frame 150 and is adaptedto be locked in any set position by means of set screws 154. The slide152 carries a blank 155 which is to be operated on by a master hob 156.The master hob 156 is mounted directly on the main frame of the machine.

The machine is operated by any suitable source of power, such forexample, as a motor 157 which is mounted on the main frame.

The armature shaft of the motor is directly connected to a shaft 158which carries a worm 159 and a pinion 160. The Worm 159 meshes with aworm wheel 161 which is mounted on the shaft 162. The shaft 162, whichis provided with bearings 163 and 164 on the main frame of the machine,carries a beveled gear wheel 165 near the end thereof. The gear wheel165 meshes with a bevel gear wheel 166 on a shaft 167. The shaft 167extends across the machine and carries gear wheels 168 and 169 near theend thereof. The gear wheel 168 meshes with a gear wheel 170 which ismounted on a short The shaft 171 is mounted on a bracket 172 whichprojects from the main frame 150 of the machine. The shaft 171 carries asecond gear Wheel 173 which meshes with a gear wheel 174 on a feed screw17 5. The feed screw 175 engages the slide 151 by any suitable nut andserves to effect longitudinal movement of such slide. Such longitudinalmovement of the slide is necessary whenever the blank and the hob beingoperated on are provided with lead.

The ear wheel 169 meshes with a gear wheel 1 6 which is mounted on ashaft 177. The shaft 177 is provided with suitable bearings on the mainframe 150 of the machine and carries a bevel gear wheel 178.

The bevel gear wheel 178 is keyed to a slide mounted on the shaft 177and meshes with a bevel gear wheel 179 on a feed screw 180. The feedscrew 180 engages a nut 181 on the slide 152 and serves to effectrelative feeding movement between the blank and the hob. In the machinedisclosed in Figs. 12 and 13 of the drawings, it will be noted the blankis fed towards the hob whereas in a machine disclosed in Figs.9 and 10of the drawings, the hob is fed towards the blank. A bracket 182, whichprojects from the slide 151, engages the bevel gear wheel 178 in orderto effect movement of such gear wheel in accordance with the movement ofthe slide 151.

The shaft 177 also carries a gear wheel 183 which meshes with a gearwheel-184 which is mounted on a shaft projecting from the frame of themachine. The gear wheel 184 meshes with teeth 185 which are formed onthe peripheryof a differential gear box 186. The function of suchgear'wheel and the differential gear mechanism will be describedhereinafter.

The pinion 160. which is mounted on the shaft 158, meshes with a gearwheel 187 which is mounted on the shaft 188. The shaft 188 is connectedto a spindle which supports the hob 156.

The shaft 158 is directly connected to one end of a'differential gearmechanism 189 and a shaft 190 is connected to the opposite end of thedifferential gear mechanism. The differential gear mechanism is of theusual and common construction and comprises two bevel gear wheels 191'and 192 which are respectively mounted on the shafts 158 and 190. Thegear wheels 191 and 192 mesh with pinions 193 and 194 which are suitablysupported in the casing 186. In such construction it is apparent if thecasing 186 is held stationary, the shaft 190 will be rotated inaccordance with the rotation of the shaft 158. Moreover, if any movementof the casing 186 is effected, corresponding variations will be effectedbetween the rotation of the shaft'158 and the shaft 190. Thedifferential gear mechanism 189 serves to vary the relative rotationbetween the hob and the blank in accordance with the feeding movementeffected between such members. The operation of such differential gearmechanism to perform such functions will be described more fullyhereinafter.

A bevel gear wheel 198 is slidably mounted on and keyed to the shaft190. An arm 199, which projects from the slide 151, en-

gages the bevel gear wheel 198 in order to effect movement of such gearwheelin accordance with the movement of the slide. The gear wheel 198meshes with a bevel gear wheel 200 which is mounted on a shaft 201. Theshaft 201 is suitably mounted on the slide 151 and-Beanies a worm member202.

The worm member 202 meshes with a worm wheel 203 which is mounted on orconnected to the spindle which supports the blank 155. By such means theblank 155 is operated in a counter-clockwise direction, as indicated inFig. 13 of the drawings. The hob 156 is rotated in a clockwisedirection, as indicated by the arrow in Fig. 13 of the drawings. Anauxiliary motor 205, which is connected to the blank spindle produces atorque opposing the action of the worm 202 in order to maintain the worm202 and the worm wheel 203 always in correct engagement with each other..The master hob 156. en-

gaging the blank 155 tends at certain periods to rotate the blank 155and take-the load off of the worm 202and the worm wheel 203. However,the torque motor 205 opposes such action and maintains a load at alltimes on the worm member 202 In the machine above described, it will benoted the hob 156 is directly connected to the motor 157 whereas theblank 155 is com nected to such motor through the differential gearmechanism 159. Moreover,1it will be noted the diflerential gearmechanism varies the rotative movement of the shaft 190 as compared'withthe shaft 158 in accordance with the operation of the shaft 167 and theshaft 177. Such shafts, as has al ready been set forth, control theoperation of the feed screw 180 and according] the relative feedingmovement between the lank and the hob. Consequently, the difl'erentialgear mechanism 189 is varied in accordance with the feeding movementsbetween the blank and the hob. Accordingly, the rotation of the blank,as compared with the rotation of the hob, is varied in accordance withthe feeding movements between such members. Thus, it is unnecessary tovary the gearing connection between the hub and the blank when thefeeding move ments are varied.

It will be-understood that such changes and modifications may be made inmy invention as fall'within the limits of the appended claims.v

What I claim is: I 1

1. A method of forming hobs, which consists in rotating a blank, inproviding a formed tool for engaging the blank, in effecting continuousrelative movement between the tool and the blank for shaping the teethon the latter, and in effecting continuous feeding movement in onedirection between the tool and the blank for relieving the teeth beingformed on the blank.

2. A method of forming hobs, which consists in rotatin a blank havingflutes cut therein, in providing a formed tool adapted .tosimultaneously cut teeth along the complete length of the blank, and inso moving the tool in one directionwith respect to the the hob and ablank as to relieve all the blank teeth in one I operation.

3. A method of, forming hobs, which consists'in rotating a blank .havingflutes cut therein, in providing a cutting tool adapted to outsimultaneously the teeth along the comtion for relieving the teethformed on the blank.

i 4. A method of forming hobs, which consists in rotating a blank havingflutes cut therein, in rotating a tool in engagement with the blank, andin effecting feeding movements between the tool andthe blank in onedirection only for relieving the teeth being formed on the blank.

5. A method of forming hobs, which consists in rotating a blank havingflutes cut therein, in rotat' a tool in engagement with the blank and intimed relation thereto for forming teeth, and in effecting continuousfeedin movement between the tool and the blank 1n one direction forrelieving the teeth bein formed on the blank.

6. A meth of forming hobs, which consists in rotating a blank havingflutes cut therein, in rotatin a tool in engagement with the blank, saidtool being rotated in timed relation to the blank rotation, and ineffecting feeding and angular advancing movement between the tool andthe blank for forming relieved teeth on the blank.

7. A met 0d of forming hobs, which consists rotating a blank havingflutes, cut therein, in rotati a tool in engagement with the blank, saidtool being rotated in timed relation to the blank rotation, and

in effecting angular advancing movement between the too and the blankwhile feeding the tool-in one direction only for forming relieved teethon. the blank.

8. method of forminghobs, which consists in providing a master hob, inrotating the hob and a lank in engagement with each other, in eifectingrelative angular advancing movement between the hob and the blank, andin effecting relative feeding movement between the hob and the blank torelieve the teeth being formed on the latter.

I 9. A method of forming hobs, which consists in providing a master hob,in rotating lank in enga ement with each other, the hob and the lankbeing rotated in opposite directions, and in rela tively movin the hoband the blank to relieve' the teet bein cut on the latter.

' 10. A method of orming hobs, which consists in providing a master hob,in rotating the hob and a blank in opposite directions and in timedrelation to each other for forming teeth, and in effecting relativefeeding movement between the hob and the blank to relieve the teethbeing cut on the latter.

11. A method of forming hobs, which epnsists in providing a master hob,in rotating the hob and a blank on. parallel axes and in speed ratio ofthe hob and the blank corresponding subst-antially to the ratio of therespective number of flutes on. th hob and the blank, and in eti'ectingrelative feeding movement between the hob and the. blank to shape andrelieve the teeth being cut 011 the latter.

13. A method of forming hobs, which consists in providing a master hob,in rotating the hob and a blank in opposite directions and in' timedrelation to each other, the hob being rotated very slightly faster thanin accordance with a speed ratio corresponding to the ratio of therespective number of flutes on the hob and the blank, and in providingrelative feeding movement between the hob and the blank to shape andrelieve the teeth being 'cut on the latter.

14. A method of forming hobs, which consists in providing a. master hob,in rotating the hob and a blank on parallel axes and in timed relationto each other for forming teeth on the blank, the hob and said blankbeing rotated in opposite directions, and in efi'ecting relative feedingmovements between the hob and the blank to shape and relieve the teethbeing formed on the latter.

15. A methodof forming hobs, which consists in providing a master hob,in rotating the hob and a blank in engagement with each other and inopposite directions, said hob being rotated in timed relation to theblank rotation, in effecting relative angular advancing movement betweenthe hob and the blank, and in effecting relative feeding movementbetween the hob and the. blank to relieve the teeth being formed on theletter.

16. A method of forming hobs, which consists in providing a master hob,in rotating the hob and a blank in timed relation to each other, eachtooth on the hob forming a predetermined tooth on. the blank and theblank and the hob being rotated in opposite directions, and inrelatively moving the hob and the blank to relieve the teeth being cuton the latter.

17. A method of forming hobs, which oon sists in providing a master hob.in rotating the hob and a. blank on parallel avesand in timed relationto each other for forming teeth on the blank, and in effecting relativefeeding movement between the hob and the blank while maintaining the twoaxes in the same plane.

18. A method of forming hobs, which consists in providing a master hob,in rotating the hob and the blank on arallel axes and in timed relationto cite other for forming teeth on the blank, and in effecting radialfeeding movement between the hob and the blan 19. A method of forminghobs, which consists in providing a master hob having teeth formedtherein by spiral flutes, in retating the master hob and a blank intimed relation to each other and in opposite directions, said blankhaving spiral flutes corresponding to the hob flutes but inclined in anopposite direction, and in relatively moving the hob and the blank torelieve the teeth being cut on the latter.

20. A method of forming hobs, which consists in providing a. master hobhaving teeth formed therein by spiral flutes, and in rotating the hoband a blank in timedrclation to each other and in opposite directions,said blank having spiral flutes corresponding to the hob flutes butinclined in an opposite direction. Y

21. A method of forming hobs, which consists in providing a master hobhaving teeth formed therein by spiral flutes, in rotating the hob and a.blank in timed relation to each other, said blank having spiral flutescorresponding to the hob flutes but inclined in an opposite direction,and in effecting relative feeding and relative angular advancingmovements between the hob and the blank to relieve the teeth beingformed on the blank.

22. A method of forming hobs, which consists in providing a master hobhaving teeth formed therein by spiral flutes, in rotating the hob and ablank in engagement with each other, said blank having spiral flutescorresponding to the hob flutes but inclined in an opposite direction,and ineffecting feeding and angular advancing movements by the hob torelieve the teeth being formed on the blank.

23. A method of forming hobs, which consists in providing a master hobhaving teeth formed therein byspiral flutes, in rotating the hob and ablank in timed relation to each other, said blank having spiral flutescorresponding to the hob flutes but inclined in an opposite direction,in effecting relative angular advancing movement between the hob and theblank, and in effecting relative feeding movement between the hob andthe blank to relieve the teeth being cut on the latter.

24. A method of forming hobs, which and in timed relation to each other,said blank having spiral flutes corresponding to the'hob flutes-butinclined in an opposite direction, and in effecting relative feedingmovement between the hob and the. blank to relieve the teeth being cuton the latter.

25. A method of forming hobs, which consists in providing a master hobhaving undercut teeth formed therein by spiral flutes, in rotating thehob and a blank'in timed relation to each other and in oppositedirections, said blank having spiral flutes. corresponding to the hobflutes but inclined in an opposite direction, and in relatively movingthe hob and the blank to relieve the teeth being cut on the latter.

26. A method of forming consists in providing a master hob havingundercut teeth formed therein by spiral flutes, in rotatin the hob and ablankon parallel axes an in timed relation to each other, said hob andblank being rotated in opposite directions, said blank having spiralflutes corresponding to the hob flutes but inclined in an oppositedirection, and in relatively feeding the hob and the blank to relievethe teeth being cut on the latter.

27. A method of forming hobs, which consists in providing a master hobhaving undercut teeth formed therein by spiral flutes, in rotating thehob and a blank in timed relation to each other, said blank havingspiral flutes corresponding to the hob flutes but inclined in anopposite direction, and in effecting relative feeding and relativeangular advancing movements be,

tween the hob and the blank to radially relieve the teeth being formedon the blank.

28. A method of forming hobs, which consistsin providing a master hobhaving undercut teeth formed therein by spiral flutes, in rotating thehob and a blank on parallel axes and in timed relation to each other,said blank having spiral flutes corresponding to the hob flutes butinclined in an opposite direction, and in effect ng relative feeding andangular advancing movements between the hob and the blank to relieve theteeth being formed on the blank.

29. A method of forming hobs, which consists in providing a master hobhaving teeth formed therein by either ,ax1al or m clined flutes, inrotating the hob and a blank in timed relation to each other and inopposite directions, said blank having axial flutes if the hob flutesare axial and flutes inclined oppositely to the hob flutes if the hobflutes are inclined, and in relatively moving the hobjand the blank torelieve the teeth being cut on the latter. g I 30. A -method of forminghobs, which consists in providing a masterhob having teethformed thereinby spiral flutes, in ro- :on parallel. axes hobs, which and in timedrelation to each other, said blank being provided with spiral flutes andundercut teeth, and in effecting relative feeding movementbetween thehob and the blank to relieve the teeth being formed on the latter. g F g31. A method of forming hobs, which consists in providing a master hobhaving 11ndercut teeth formed therein'by spiralflutes, in rotating thehoband a blank on parallel axes and in timed relation toeach other, saidhob and the blank being rotated in opposite directions, said blankhaving spiral flutes corresponding to the hob flutes but inclined in anopposite direction, the blank being engaged along its whole length bythe hob, and in effecting relative feeding movement between the hob andthe blank to shape and relieve the teeth beingcut on the latter. 32. Amethod of forming hobs, which consists in providing a master hob and ablank of the same number of flutes, the diameter of the" hob beinggreater than the diameter of the blank, in rotating the hob and theblank on parallel axes at substantially the same number of revolutionsand in opposite directions, and in effecting relative feeding movementbetween the hob and the blank to shape and, relieve the teeth beingformed on the latter.

33.- A method of forming hobs, which consists in providing a master hoband a blank having the same number of flutes, inrotating the hob and theblank on parallel axes at substantially the same speeds, the hob and theblank being turned in opposite directions similarly to two intermeshinggear wheels, the hob having a larger diameter than the blank to effect acutting action, in rotating the hob a trifle faster than the blank toangularly advance the hob with respect to the blank, and in effectingradial responding gear wheel in order to effect a.

cutting action, in rotating the hob a trifle faster than in accordancewith a speed ratio corresponding'to theratio of the number of flutes onthe hob and the blank to angularly advance the hob with respect to. theblank, and in effecting radial, feeding, movement between thehob andthebla'nk in timed relation to the sai'dan'giilar advance of the hob,{)0 shape and relieve .the teeth out on'the lanr.. y Y

35. A method of forming a hob from a blank having a predetermlned numberof flutes, which consists in providing a master hob having apredetermined number of flutes, the number of flutes on the hob and theblank being so chosen as to containa common factor different from one,in rotating the master hob and the blank on parallel axes in timedrelation to each other, the speed ratio between the hob and the blankcorresponding substantially to the ratio of the respective number offlutes on the hob and the blank, each tooth of the master hob cuttingonly predetermined teeth, on the' blank, and in efl'ecting' relativefeeding movement between the hob and the blank to shape and relieve theteeth out on the latter.

36. A method of forming hobs, which consists in providing a master hobhaving an even number of flutes, said flutes forming teeth and the teethformed by each flute being staggered with respect to the teeth formed/bythe adjacent flutes, in providing a blank with an even number of flutes,in rotating the hob and the blank about parallelaxes in timed relationtoeach other, the speed ratio between the hob and the blankcorresponding substantiallyto the ratio of the respective numbers offlutes on the hob and the blank, and in effecting a relative feedingmotion between the hob and the blank to shape and relieve the thread cuton the latter in one continuous operation. 37. A method of forming hobs,which consists in providing a master hob having teeth formed therein byeither axial or inclined flutes, in rotating the hob and a blank intimed relation to each other and in opposite directions, said blankhaving axial flutes if the bob flutes are axial and flutes inclinedoppositely to the hob flutes if the hob flutes are inclined, ineffecting relative angular advancing movements between the hob and theblank, and in relativelymov ing the hob and the blank to relieve theteeth being cut on the latter. a

38. A method of forming hobs, which consists in providing a master hobhaving teeth formed therein by either axial or inclined flutes, inrotating the hob and a blank in timed relation to each other and inopposite directions, said blank having axial flutes if the hob flutesare axial and flutes inclinedoppositely to the hob flutes if the hobflutes are inclined, in effecting angular advancing movements by the hobwith respect to the blank, and in radially feeding the hob with respectto the blank for relieving the teeth being cut on the later.

39. A method of forming hobs, which consists in providing a master hobhaving teeth thereon in the form of a thread having a predeterminedlead, in rotating the hob and a blank in timed relation to each otherand in opposite directions, andin effecting relarections, the diameterof the the hob but in an opposite direction.

40. A method of forming hobs, which conon in the form of a thread havinga predetermined lead, in rotating the hob and a blank in engagement witheach other and in opposite directions, and in eflecting relative axialmovement between the hob and the blank for formin a thread having thesame lead as the thread on the hob but in an opposite direction, and ineflecting relative angular advancing movement by the hob with respect tothe blank.

41. A method of forming hobs, which consists in providing a hob havingteeth thereon in the form of a thread having a predetermined lead, inrotating the hob and a blank in engagement with each other and inopposite directions, and in effecting relative axial movement betweenthe hob and the blank for forming a thread having the same lead as thethread on the hob but in an opposite direction, and in effecting lateralfeeding movements by the hob with respect to the blank for relieving theteeth being cut on the blank. t

42. A method of forming hobs, which consists in providing a hob havingteeth thereon in the form of a thread having a predetermined lead, inrotating the hob and a blank in engagement with each other and in oposite directions, in forming a thread on t e blank with the same leadas the hob thread .sists in providing a hob having teeth therebut in anopposite direction while efl'ecting relative angular advancing movementsby the hob with respect to the blank, and in effecting feeding ovementsby the'hob for relieving the teet being formed on the blank.

43. A method of forming hobs, which consists in providing a hob havingteeth thereon in. the form of a thread having a predetermined lead, inrotatin the hob in engagement with a blank an in opposite diob beinglarger than the diameter of the blank, in effecting relative axialmovement between the hob and the blank for forming a thread having thesame lead as the thread on the hob but in an opposite direction, ineffecting relative angular advancing movement's by the .hob with respectto the blank, and in effecting radial feeding movements by the hob withrespect to'the blank for relieving l the hob and the blank for forming athread having the same lead as the thread on the thereon in t e form ofa thread havin a predetermined lead, the teeth on said ob being formedby flutes which are inclined with respect to the hob axis, in rotatlngthe hob and a blank in engagement with each other, said blank havingflutes therein which are inclined in an op osite direction to the fluteson the hob, an in forming a thread on the blank with the same lead asthe hob thread but in an opposite direction while I 1 sists in providingeffecting angular advancin movements between the hob and the bla 46. Amethod of-forming a hob, whic consists in providing a hob having teeththereon in the form of a thread havin a predetermined lead, the teeth onsaid ob being formed by flutes WlllCll are inclined with respect to thehob axis, in rotating the hob and a blank in engagement with each other,said blank having flutes therein which are inclined in an oppositedirection to the flutes on the hob, in blank with the same lead as thehob thread but in an opposite direction, and in effectin relativefeeding movements between the ho and the blank for relieving the teethbeing formed.

47. A method of forming hobs, which consists in providing a hob havingteeth thereon in the form of a thread having a predetermined lead, theteeth on said hob being formed by flutes which are inclined with respectto the hob axis, in rotating the hob and a blank in engagement with eachother, said blank having flutes therein which are inclined in anopposite direction to the flutes on the hob, and in forming a thread onthe blank with the same lead as the hob thread but in an oppositedirection while .efiecting relative feeding and angular advancingmovements between the hob and the blank to relieve the'teeth beingformed.

48. A method of forming a hob, which consists in providing a hob havingteeth thereon in the form of a thread having a predetermined lead, theteeth on said ob being formed by spiral flutes, in rotating the hob anda blank in engagement with each other, said blank having flutes thereinwhich are inclined in an opposite direction to the flutes on the hob, informing a thread on the blank with the same lead as the hob thread butin an opposite direction,

and in effecting relative feeding and .ad-

orming a thread on the vancing movements between the hob and the blanktorelieve the teeth being formed.

49. A method offorming hobs, which consists in providing a hob having'teeth thereon in theform of a thread. havin a predetermmed lead, theteeth on said iob being formed by flutes which are inclined with respectto the hob axis, in rotating the hob and a blank in engagement with eachother and in opposite directions, said blank having flutes therein whichare inclined in an op -'posite direction to the flutes on the hob, in

formin a thread on the blank with the same lead as the hob thread but inan opposite direction while eflecting relative angular advancingmovements between the hob and the blank, and in eifecting relativefeeding movements between the hob and the blank to relieve the teethbeing formed.

50. A method of forming hobs, which cona hob having teeth thereon 1n theform of a thread havin -a predetermmed lead, the teeth on said %l0bbeing formed by flutes which are inclined with respect to the hob axis,in rotating the hob an a blank in engagement with each other and mopposite directions, said blank havlng flutes therein which are inclinedin an opposlte direction to the flutes on the hob, in forming a threadon the blank with the same lead as the hob thread but in an oppositedirection, while efl'ecting relative angular advancing movements by thehob with respect to the blank, and in effecting feedlng movements by thehob for relieving the teeth being formed on the blank.

51. A method of forming hobs, which consists. In providing a master hobhaving teeth formed in a thread by means of flutes, the teeth formed byeach flute bjeing sta gered w th respect to the teeth formed by tie adjacent flutes, in rotating the hob in engagement with a blank havingcorrespondin flutes cut in it, and in eifecting feeding an angularadvancing movements between the hob and the blank for forming relievedteeth gnbthe blank similar to the teeth on the 52. A method of forminghobs, which consists in providing a master hob having teeth formed in athread by means of flutes, the

teeth formed by each flute being staggered with respect to the teethformed by the adjacent flutes, in rotating the hob in engagement with ablank having corresponding flutes cut in it, said hob and blank beingrotated in opposite directions, and in effecting feeding and an laradvancing movements between the ob and the blank for forminr relievedteeth on the blank similar to the teeth on the hob.

53. A method of forming hobs, which consists in providing a master hobhaving teeth formed in a thread by means of flutes, the

teeth formed by each flute being sta gered with respect to the teethformed by t e adjacent flutes, in rotating the hob in engagement with ablank having corresponding flutes out in it, in effecting angularadvancing movements by the hob with respect to the blank, and ineffecting feeding movements by the hob for relieving the teeth beingformed onthe blank.

54. A method of forming hobs, wh1ch consists in providing a master hobhaving teeth formed in a thread by means of flutes, the teeth formed byeach flute being staggered with respect to the teeth formed by adjacentflutes, in rotating the hob in engagement with a blank havingcorresponding flutes cut in it,-said hob and the blank being rotated inopposite directions, in efi'ectin angular advancing movements by the howith respect to the blank, and in effecting feeding movements by the hobfor relieving the teeth being formed on the blank.

55. A method of forming hobs, which consists in providing a master hobhaving rows of teeth formed by flutes, the teeth formed by each flutebeing staggered with respect to the teeth formed by the adjacent flutes,in rotating the hob in engagement with a blank having correspondingflutes out in it, and in effecting 'feeding and angular advancingmovements between the hob and the blank for forming relieved teeth onthe blank similar to the teeth on the hob.

56. A method'of forming hobs, which consists in providing a master hobhaving rows of teeth formed by flutes, the teeth formed by each flutebeing staggered with respect to the teeth formed by the adjacent flutes,in rotating the hob in engagement with a blank having correspondinflutes cut in 1t, said hob and the blank being rotated in opposite.directions, in effecting an ular advancing movements by the hob witrespect to the blank, and in effecting feeding'movements by the hob forrelieving the teeth being formed on the blank. i

57. A method of forming hobs, which consists in providing a master hobhaving teeth formed in a thread by means of flutes, the teeth formed byeach flute being staggered with respect to the teeth' formed by theadjacent flutes, in rotating the hob in engagement with a blank havingcorresponding flutes cut in it, said hob and blank being rotated inopposite directions and having differentdiameters, and in effectingfeeding and angular advancing movements between the hob and the blankfor forming relieved teeth on the blank similar to the teeth on the hob.

58. Amethod of forming hobs, which consists in providing a master hobhaving teeth provided with non-radially arranged cutting faces formed byflutes, in rotating the master hob and a blank in engagement with eachother and in opposite directions, said blank having flutes cut in itsimilar to the flutes in the master hob, in eifecting angular advancingmovements between the hod and the blank, and in effecting relativefeeding movements between the'hob and the blank to relieve the teethbeing formed on the latter.

59. A method of forming hobs, which consists in providing a master hobhaving teeth provided with non-radially arranged cutting faces formed byflutes, in rotating the master hob and a blank in engagement with eachother and in opposite directions, said blank having flutes cut in itsimilar to the flutes in the master hob, in effecting angular advancingmovements between the hob and the blank, and in effecting relativefeeding movements between the hob and the blank to radially relieve theteeth being formed on the latter.

60. A method of forming hobs, which con sists in providing a master hobhaving teeth provided with non-radially arranged cut. ting faces formedby flutes, in rotating the master hob and a blank in engagement witheach other, said blank having flutes cut in it similar to the flutes inthe master hob, in eflecting angular advancing movements by the masterhob with respect to the blank, and in eflecting feeding movements by themaster hob to radially relieve the teeth being formed on the blank.

61. A method of forming hobs, which consists in providing a hob havingundercut teeth thereon in the form of a thread having a predeterminedlead, the teeth on said hob being formed by flutes which are inclinedwith respect to the hob axis, in rotating the hob and a blank inengagement with each other, said blank having flutes therein which areinclined in an op osite direction to the flutes on the hob, and informing a thread on the blank with the same lead as the hob thread butin an'opposite direction.

62. A method of forming hobs, which consists in providing a hob havingundercut teeth thereon in the form of a thread havin a redeterminedlead, the teeth on'said ho being formed by flutes which are inclinedwith respect'to the hob axis, in rotating the hob and a blank inengagement with each other and in opposite directions, said blank havingflutes therein which are inclined in an opposite direction to the fluteson the hob, in forming a thread on the blank with the samelead as thehob thread but in an opposite direction, and in effecting feeding andangular advancing movements between the hob and the blank for relievingthe teeth being formed on the latter.

63. A method of forming hobs, which consists in providing a master hobhaving unhob multiplied by the ratio of the respective hob in timedrelation to the rotation of the dercut teeth formed therein by flutes,in rotating the master hob and a blank in engagement with each other andin o posite directions, said blank having flutes ormed therein similarto the flutes in the hob, and in relatively moving the hob and the blankto relieve the teeth being cut on the latter.

'64. A method of forming hobs, which consists in providing a master hobhaving undercut teeth formed therein by flutes, in rotating the hob inengagement with a blank having flutes similar to the hob flutes cuttherein, the diameter of the blank being difl'erent from the diameter ofsaid hob, the hob and the blank being rotated'in opposite directions,and in efiecting feeding and angular advancing movements by the blank.

65. A method of forming hobs, which consists in providing a master hobhaving un dercut teeth formed therein by either axial or inclinedflutes, in rotating the master hob and a blank in engagement with eachother and in opposite directions, said blank having similar axial flutesif the hob flutes are axial and similar flutes inclined oppositely tothe hob flutes if the hob flutes are inclined, ineflecting relativeangular advancing movements between the hob and the blank, and inrelatively moving the hob and the blank to relieve the teeth being cuton 1 tion-to each other, said hob and the blank the latter.

66. A method of forming hobs, which consists in providing a master-hobhaving teeth arranged in the form of a thread having a predeterminedlead, in rotating the hob andablank on parallel axes and in timedrelation to each other, said hob and blank being rotated in oppositedirections and the speed ratio of the hob and the blank correspondingsubstantially to the ratio of the number of threads on the hob and thenumber of threads to be formed on the blank, and in eflecting relativefeeding movement between the hob and the blank for forming a threadhaving a lead, said thread'having a lead equal to the lead of the masternumber of threads on the blank and the hob and in an opposite directionas compared with the lead of the hob thread.

67. A method of forming hobs, which consists in providing a master hobhaving teetli' thereon in the form of a single thread having apredetermined lead, in rotating the hob and a blank on parallel axes andin timed relation to each other, said hob and blank being rotated inopposite directions and the speed ratio of the hob and the blankcorresponding substantially to'the number.

of threads to be cut on the blank, and in effecting relative teedinmovement between fbr forming a thread the hob and the blank tion to eachother, said hob and the blank being rotated in opposite directions andthe speed ratio of the hob and the blank corresponding substantially tothe ratio of the respective number of threads on the hob and thethreadsto be formed onthe blank, the

hob running a trifle faster than would cor-' respond to the exact ratioof the respective number of threads on the hob and the blank toefl'ectan angular advance thereof, and in efl'ectingrelative feeding movementbetween the hob and the blank for forming a thread having a lead,said'thread having a lead equal tothe lead of the master hob multipliedby the ratio of the respective number of threads on the blank and thehob and in an opposite direction as the lead of the hob thread.

69. A method of forming hobs, which consists in providing a master hobhaving teeth compared with thereon in the form of a thread having a"predetermined lead, in rotating the hob and a blank on parallel axes andin timed rela-.

on the blankand the hob and in an opposite direction as compared withthe lead of the hob thread.

70. A method of forming hobs, which consists in providing a master hobhaving teeth m the form of a thread having a predetermined lead, inrotating the hob and a blank on parallel axes and in timed relation toeach other, said hob and the blank being rotated in opposite directionsand at substantially the same rotative speed, the master hob running atrifle faster than the blank to efl'ect an angular advance with everyrevolution, the

diameter of the master hob being larger than the diameter of the blank,and in efl'ecting relative axial feeding movement-between the hob andthe blank for forming a hob of the same lead and the same number ofthreads as the master hob, the thread bein however of opposite directioncompared wit the lead of the master hob.

